This invention involves a gear mechanism for tandem axles of work vehicles, particularly those designed for use in difficult terrain, with a gear drive for equal power transmission to the front and rear wheels of one side of a tandem axle.
Work vehicles with which the invention finds utility are, for instance, trucks used in forestry, including those equipped with saws, gripping equipment, branch-removal equipment and/or transport mechanisms.
Various types of gear mechanisms for tandem axles are well-known in present-day technology. It is possible, for example, to differentiate between tandem axles with gear drives and tandem axles with chain drives. In the case of tandem axles with gear drives, there are designs both with and without planetary gearing. The disadvantages of the latter design type are the limited ground clearance of the tandem axle housing, caused by the missing terminal reduction and the related large diameter of the rear wheels, as well as their heavy weight, since wide gear wheels are required. A further disadvantage lies in the fact that because of the torque direction only one rear intermediate gear wheel can be used, thus limiting the gear reduction to a maximum of 1.8 to 2.2. Furthermore, no brake retarding circuit is possible to the left or right of the differential, since, because there is no gear box reduction, it is necessary to have a large spur bevel gear in the differential or to have an additional two planetary gears installed next to the differential.
An advantage of the known tandem axles with gear wheels and without a planetary end stage is the fact that the lift effect of the tandem axle is slight because of the low gear reduction, and a uniform stress is thus put on the front and rear wheels. The lift effect becomes especially bad when, because of ground conditions, one of the tandem wheels becomes blocked, or is braked more strongly than the other wheel of the same axle and thus causes this wheel to lift up and lose its grip on the road. In the case of tandem axles with gear wheels and a planetary gear design, as, for example, described in DE-OS 25 22 542 and EP 01 80 585, this lift effect is also great because of the high gear reduction, which also leads to an unequal stress on the single gear, in which case the torque can disadvantageously be 100% on one side. The advantage of this design type is the fact that small, narrow gear wheels can be used, thus reducing the overall weight. Furthermore, use of a small rear wheel produces good ground clearance for the tandem boxes.
It is likewise possible to differentiate between design types with and without planetary gear end stages for the also well-known tandem axles with chain gears. These have the same kind of advantages and disadvantages as tandem axles with gear wheels.